The present invention relates generally to a printing machine, and more particularly to a printing machine provided with a sheet-transfer arrangement for transferring sheets between printing stations of the machine.
It is known to provide printing machines, particularly multi-color printing machines, with a plurality of printing stations each of which has a printing roller. In order to be able to print in such machines on both sides of a sheet it is necessary to reverse the sheet as it travels from one printing station to the next. For this purpose, a sheet transfer roller is employed which picks the trailing edge of the sheet off the printing roller of one printing unit, and thereupon reverses the sheet side for side as it conveys the sheet to the printing roller of the next printing unit. The engagement of the sheet is effected by a suction gripper system which furnishes the engaged trailing edge of the sheet with a mechanical gripper system. This arrangement is disclosed in GDR Pat. No. 54,703 and is generally satisfactory. However, in case of high-spped operation, for example 8000 sheets per hour or more, and given a certain characteristic of the sheets, it is possible for the sheets to change their proper orientation in this arrangement because the suction gripper system must move the entire sheet relative to the rotation of the printing cylinder from which it picks the sheet up.